mm: numa: Scan pages with elevated page_mapcount

Currently automatic NUMA balancing is unable to distinguish between false
shared versus private pages except by ignoring pages with an elevated
page_mapcount entirely. This avoids shared pages bouncing between the
nodes whose task is using them but that is ignored quite a lot of data.

This patch kicks away the training wheels in preparation for adding support
for identifying shared/private pages is now in place. The ordering is so
that the impact of the shared/private detection can be easily measured. Note
that the patch does not migrate shared, file-backed within vmas marked
VM_EXEC as these are generally shared library pages. Migrating such pages
is not beneficial as there is an expectation they are read-shared between
caches and iTLB and iCache pressure is generally low.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-28-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 6 insertions, 11 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 7bd90d3b16bb..fcba2f46bb80 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1599,7 +1599,8 @@ int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
  * node. Caller is expected to have an elevated reference count on
  * the page that will be dropped by this function before returning.
  */
-int migrate_misplaced_page(struct page *page, int node)
+int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
+                           int node)
 {
         pg_data_t *pgdat = NODE_DATA(node);
         int isolated;
@@ -1607,10 +1608,11 @@ int migrate_misplaced_page(struct page *page, int node)
         LIST_HEAD(migratepages);
 
         /*
-         * Don't migrate pages that are mapped in multiple processes.
-         * TODO: Handle false sharing detection instead of this hammer
+         * Don't migrate file pages that are mapped in multiple processes
+         * with execute permissions as they are probably shared libraries.
          */
-        if (page_mapcount(page) != 1)
+        if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
+            (vma->vm_flags & VM_EXEC))
                 goto out;
 
         /*
@@ -1661,13 +1663,6 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
         int page_lru = page_is_file_cache(page);
 
         /*
-         * Don't migrate pages that are mapped in multiple processes.
-         * TODO: Handle false sharing detection instead of this hammer
-         */
-        if (page_mapcount(page) != 1)
-                goto out_dropref;
-
-        /*
          * Rate-limit the amount of data that is being migrated to a node.
          * Optimal placement is no good if the memory bus is saturated and
          * all the time is being spent migrating!